The present invention relates to a rolling-element bearing such as a roller bearing, in which a rolling element is retained in each of retaining openings in a retainer, and to a method and an apparatus for manufacturing the rolling-element bearing. More specifically, the present invention pertains to a rolling-element bearing that has retaining pieces for preventing rolling elements from falling off at the edges of the retaining openings, and to a method and an apparatus for manufacturing the rolling-element bearing.
Conventionally, methods for manufacturing roller bearings have been disclosed, for example, in Japanese Laid-Open Patent Publication No. 10-115322, Japanese Laid-Open Patent Publication No. 7-151153, and Japanese Laid-Open Patent Publication No. 2000-18258. According to the manufacturing method disclosed in Japanese Laid-Open Patent Publication No. 10-115322, the outer circumferential surface and the inner circumferential surface of a retainer are pressed simultaneously to form retaining pieces at the edges of each retaining opening on the outer circumferential surface and the inner circumferential surface. Japanese Laid-Open Patent Publication No. 7-151153 and Japanese Laid-Open Patent Publication No. 2000-18258 each disclose a manufacturing method in which projections formed on the inner side faces of each retaining opening are subjected to ironing to form retaining pieces at the edges of the retaining opening on the outer circumferential surface and the inner circumferential surface. Specifically, each retaining piece is formed by pressing the distal portion of a projection on the inner side face of the retaining opening in the direction of thickness of the retainer, thereby partially thinning the projection.
The above described conventional methods have the following drawbacks.
In the manufacturing method disclosed in Japanese Laid-Open Patent Publication No. 10-115322, when forming retaining pieces on the retainer, pressing force applied to the periphery of each retaining opening can cause the inner side faces of the retaining opening to bulge into the retaining opening. This narrows the width of the retaining openings, and thus hampers smooth rotation of rollers.
Also, according to the manufacturing methods disclosed in Japanese Laid-Open Patent Publication No. 7-151153 and Japanese Laid-Open Patent Publication No. 2000-18258, the strength of the retaining pieces cannot be sufficiently ensured because the retaining pieces are formed through ironing. Therefore, the rollers cannot be stably retained in the retaining openings for an extended period of time.